1. Field of the Invention
This invention relates to an auto-focusing device for a camera.
2. Description of the Prior Art
Heretofore, various kinds of auto-focusing devices have been proposed wherein reference light is irradiated on an object via a flood optical system. Reflected light from said object is received on a fixed photosensor such as a PSD (position sensitive detector) via a light-receiving lens. The light-receiving position of said reflected light on said photosensor is detected from an output of the photosensor to determine the distance from the object. Adjustment of the focus is performed by driving the lens from the initial position thereof by a length in accordance with the determined distance.
In devices as described above, the amount of movement of the lens from its initial position can be uniquely determined in accordance with the light-receiving position of the reflected light on the surface of said photosensor. Hence, lens drive control has been performed by storing in a storage device a standard, general relationship between the light-receiving position of the reflected light on the surface of said photosensor and the drive amount of the lens and by detecting, when performing the auto-focusing operation, the light-receiving position of the reflected light on said photosensor, and by reading a drive amount in accordance with said light-receiving position from the storage device.
Since the relationship between the light-receiving position and the drive amount of the lens can be basically determined in a unique fashion, the information on each lens drive amount to be stored in said storage device with regard to each light-receiving position can be fixed at a constant value.
Actually, however, it is necessary to calibrate a relationship between the light-receiving position and the lens drive amount, due to variations from the proper photosensor fixing position while mounting said photosensor in the camera and or variations in the accuracy of the output from each photosensor. Heretofore, the relationship between the light-receiving position and the lens drive amount must be calibrated by finely adjusting the fixing position of the photosensor.
In the conventional method in which calibration is performed by finely adjusting the position of the photosensor as described above, the mechanism for the position adjustment of the photosensor becomes necessarily complicated in order to perform the calibration with a high accuracy, resulting in a larger camera configuration and/or a complication of camera handling.